Thermoplastic, branched aromatic polyphosphonates, and a process for their production

ABSTRACT

Thermoplastic, branched aromatic polyphosphonates with average molecular weights (number average M n ) of from 11,000 to more than 200,000, obtainable by transesterifying (a) from 97 to 100 moles of at least one diaryl phosphonate, and (b) from 0 to 3 moles of at least one triaryl phosphate--the sum of the moles of (a) and (b) being 100--with (c) from 90 to 99 moles of at least one aromatic dihydroxy compound, and (d) from 0 to 3 moles of at least one aromatic trihydroxy or tetradhydroxy compound--with the proviso that at least one of the components (b) and (d) is present in a quantity of at least 0.001 mole and that, where (b) and (d) are used, the maximum limit on the moles is 3.0.

This application is a division of application Ser. No. 160,646 filedJune 18, 1980 now U.S. Pat. No. 4,331,614.

This invention relates to thermoplastic, branched aromaticpolyphosphonates having average molecular weights (number average M_(n))of from about 11,000 to more than 200,000, to a process for theirproduction by transesterification and to the use of thesepolyphosphonates for the production of thermoplastic mouldings.

It is known that linear aromatic polyphosphonates can be produced bycondensing aryl phosphonic acid dichlorides and aromatic diol compoundsin a solvent either in the absence of a catalyst or in the presence ofalkaline-earth metal halides as catalyst as is described in U.S. Pat.Nos. 3,946,093 and 3,919,363. The polyphosphonates are recovered fromthe solutions obtained either by precipitation with methanol or byevaporating off the solvents. In either case, linear polyphosphonates ofrelatively low molecular weight (M_(n) 6000 to 11,000) are obtained,still containing residues of organically bound chlorine (cf. ComparisonExample 1 of the present application). They may be used as flameproofingadditives for plastics. Polyphosphonates of this type are unsuitable foruse as starting materials for the production of thermoplastic mouldingsboth because of their excessively low molecular weight and because oftheir residual chlorine content which can be split off or hydrolysed atelevated temperature.

According to U.S. Pat. No. 4,046,724, linear polyphosphonates havingaverage molecular weights (M_(n)) of from 300 to 70,000 are said to becombined with polyalkylene terephthalates in order to improve theirflame resistance. This U.S. patent specification does not contain anymention of the process by which the linear polyphosphonates of highmolecular weight are produced. The Examples of this U.S. patent refersolely to polyphosphonates which have an average molecular weight(M_(n)) of at most 12,000.

In addition, it is known from U.S. Pat. No. 2,682,522 that phosphonicacid diaryl esters may be transesterified with aromatic dihydroxycompounds in the melt at 100° C. to 400° C. in the presence of catalyticquantities of anhydrous alkaline-earth metal halides initially atatmospheric pressure and then under reduced pressure to form linear,aromatic polyphosphonates, the volatile constituents being removed bydistillation. In this case, too, the polymers obtained do not have thehigh molecular weight required for use as chemical materials. In thisprocess, the velocity of the transesterification reaction in the melt isso low that it is not possible to obtain commercially useful polymershaving a sufficiently high degree of condensation (cf. also ComparisonExample 2 of the present application).

Finally, it is known inter alia from U.S. Pat. No. 2,716,101 that alkylor aryl phosphonyl dichlorides, aromatic dihydroxy compounds andphosphorus oxychloride or phenyl dichlorophosphate can be condensed inthe presence of anhydrous magnesium chloride with the elimination ofhydrogen chloride and phenol to form polyphosphonates containingphosphate groups as branching sites. Although the rubber-like polymersobtained may formally contain structures as indicated under A and B ofthe present application (where c=0, a=1, b=1 and R² =X), they differfrom the polyphosphonates according to this invention in that they haveaverage molecular weights (number average M_(n)) of far less than 11,000and are unsuitable for the production of mouldings having high thermalstabilities under load and outstanding mechanical properties, as alsoshown by Comparison Examples 3 and 4 of the present application.

The hitherto known linear aromatic polyphosphonates are always used asadditives for other polymers in order to improve the flame resistance ofthe mixtures thus obtained.

The object of the present invention is to provide thermoplasticpolyphosphonates which may be used as such, i.e. without the addition ofother polymers, for the production of mouldings characterised by highflame resistance, high thermal stability under load and outstandingmechanical properties.

According to the invention, this object is achieved in that, startingalways from materials having a purity of more than 99.1% and preferablymore than 99.7%, diaryl phosphonates which may contain small quantitiesof triaryl phosphates are transesterified with aromatic dihydroxycompounds, which may be mixed with small quantities of at leasttrifunctional, aromatic hydroxy compounds (one of the two branchingagents, triaryl phosphate and the at least difunctional aromatic hydroxycompounds, must be present in the reaction mixture) in the presence ofbasic catalysts to form aromatic branched polyphosphonates havingaverage molecular weights (number average M_(n)) of at least 11,000.

Accordingly, the present invention relates to thermoplastic, branchedaromatic polyphosphonates with average molecular weights (number averageM_(n)) of from 11,000 to more than 200,000, consisting of recurringunits of the following structures: ##STR1##

(C.) the terminal members bound to phosphorus in the structures A and B##STR2## and the terminal members bound to oxygen ##STR3## (the symbolsX, D, p and R¹ are defined below), the proportion of (B.) based on thesum of A and B, amounting to between 0.001 and 3 mole percent; thesymbols used in the structures and formulae have the following meanings:

R¹ represents at least one of the radicals;

C₁ -C₁₂ alkyl;

C₂ -C₁₂ alkenyl;

C₆ -C₃₀ cycloalkyl, cycloalkenyl, aryl, arylalkyl or arylalkenyl, thearyl group in each case being unsubstituted or substituted by 1 to 5 C₁-C₄ alkyl groups or by 1 to 5 halogen atoms (fluorine, chlorine orbromine) or by the above-mentioned alkyl groups and halogen atoms;

X represents at least one of the following radicals:

    ______________________________________                                        phenylene                                                                                       ##STR4##                                                    biphenyl                                                                                        ##STR5##                                                    C.sub.1 -C.sub.4 alkylene bis-phenylene                                                         ##STR6##                                                    C.sub.5 -C.sub.12 cycloalkylene bis-phenylene                                                   ##STR7##                                                    thiobis-phenylene                                                                               ##STR8##                                                    oxy-bis-phenylene                                                                               ##STR9##                                                    sulphonyl-bis-phenylene                                                                         ##STR10##                                                   carbonyl-bis-phenylene                                                                          ##STR11##                                                   naphthylene                                                                                     ##STR12##                                                   ______________________________________                                    

each phenyl nucleus being unsubstituted or substituted by 1 to 4 C₁ -C₄alkyl groups or by 1 to 4 halogen atoms (fluorine, chlorine or bromine)or by the above-mentioned alkyl groups and halogen atoms and thenaphthylene nucleus being unsubstituted or substituted by 1 to 6 of atleast one of the above-mentioned groups or atoms;

Y represents a trifunctional or tetrafunctional residue of atrifunctional mononuclear or trifunctional or tetrafunctionalpolynuclear phenol from which the phenolic hydroxyl groups have beenremoved in the case of the polynuclear phenol, the aromatic nucleicarrying one or two phenolic hydroxy groups are connected by aliphaticC₁ -C₇ hydrocarbon radicals or by at least one benzene radical;

Y represents X where c=0, a=1, b=1 and, at the same time, R² ═Y'--O--X--O--)_(c'), or

R² ═X with Y'═Y and c'=1 or 2;

a=0 or the number 1;

b=0 or the number 1;

c=0 or one of the numbers 1 or 2, preferably c=1 or 2;

R² ═R¹ where a and b are each 0, in which case Y must represent atrifunctional or tetrafunctional radical, as defined above;

R² represents ##STR13## where a=1 and b=0, in which case Y mustrepresent a trifunctional or tetrafunctional radical, as defined above;

R² represents X or Y'--O--X--O)_(c') where a and b are each the number1;

D represents the same or different groups and represents a C₁ -C₄ alkylgroup or halogen (F, Cl or Br) and p=0 or a number of from 1 to 5,preferably p=0.

The above definitions preferably have the following meaning:

R¹ represents at least one of radicals methyl or phenyl, particularlymethyl;

X represents at least one of the radicals phenylene, biphenylylene, C₁-C₄ alkylene bisphenylene, in which case each phenyl nucleus may besubstituted by 1 to 4 methyl groups, cyclohexylene-bis-phenylene,oxy-bis-phenylene, thio-bis-phenylene, sulphonyl-bis-phenylene,particularly C₁ -C₄ alkylene-bis-phenylene, in which case each phenylnucleus may be substituted by one or two methyl groups;

Y represents a trifunctional or tetrafunctional residue of atrifunctional mononuclear or trifunctional or tetrafunctionalpolynuclear phenol from which the phenolic hydroxyl groups have beenremoved; in the case of the polynuclear phenol, the aromatic nucleicarrying one or two phenolic hydroxy groups may be connected byaliphatic C₁ -C₇ hydrocarbon radicals or by at least one benzeneradical;

a=0 or the number 1;

b=0 or the number 1;

c=one of the numbers 1 or 2;

R² =R¹ where a and b are each 0;

R² represents ##STR14## where a=1 and b=0;

R² represents X or Y'--O--X--O--)_(c') where a and b are each the number1;

D represents the same or different groups and represents a C₁ -C₄ alkylgroup and p=0 or a number of from 1 to 5, more particularly p=0.

The thermoplastic, branched aromatic polyphosphonates according to theinvention preferably have average molecular weights (number averageM_(n)) of from 13,000 to 80,000 and more particularly from 13,000 to40,000. The molecular weights are determined by membrane osmosis usingmembranes which are permeable to particles having a molecular weight ofup to 3,000.

The present invention also relates to a process for the production ofthermoplastic, branched aromatic polyphosphonates having averagemolecular weights (number average M_(n)) of from 11,000 to more than200,000 by transesterification which is characterised in that

(a) from 97 to 100 moles of at least one diaryl phosphonate and

(b) from 0 to 3 moles of at least one triaryl phosphate, the sum of themoles of (a) and (b) being 100,

are transesterified with

(c) from 90 to 99 moles of at least one aromatic dihydroxy compound and

(d) from 0 to 3 moles of at least one aromatic trihydroxy ortetrahydroxy compound--with the proviso that at least one of thecomponents (b) and (d) is present in a quantity of at least 0.001 moleand that, where (b) and (d) are used, the maximum limit on the moles is3--in the melt at 90° C. to 340° C. in an oxygen-free gas atmosphereeither at atmospheric pressure or under reduced pressure and in thepresence of from 10⁻⁵ to 5.10⁻² mole percent, based on 100 mole percentof aromatic dihydroxy compound, of at least one basic catalyst, thevolatile constituents being removed by distillation.

The transesterification reaction is preferably carried out withcomponents (a), (b), (c) and (d), component (a) being used in quantitiesof from 98.5 to 99.999 moles, more particularly in quantities of from99.25 to 99.975 moles, component (c) being used in a quantity of from 93to 97 moles and components (b) and (d) each being used in quantities offrom 0.001 to 1.5 moles and, more particularly, in quantities of from0.025 to 0.75 mole.

Phosphonic acid diaryl esters corresponding to formula I below arepreferably used for transesterification. ##STR15## In this formula:

R¹ represents at least one of the following radicals:

C₁ -C₁₂ alkyl,

C₂ -C₁₂ alkenyl,

C₆ -C₃₀ cycloalkyl, cycloalkenyl, aryl, arylalkyl or arylalkenyl, thearyl group in each case being unsubstituted or substituted by 1 to 5 C₁-C₄ alkyl groups or by 1 to 5 halogen atoms (F, Cl or Br) or by theabove-mentioned alkyl groups and halogen atoms;

Z represents F, Cl, Br or C₁ -C₄ alkyl and several Z's in one arylradical are the same or different, and

m=0 or an integer of from 1 to 5.

It is particularly preferred to use methy or phenyl phosphonic aciddiphenyl ester.

Preferred aromatic dihydroxy compounds correspond to formulae II and IIIbelow ##STR16## in which

A' represents a single bond, an alkylene group containing from 1 to 4carbon atoms, a cycloalkylene group containing 5 or 6 carbon atoms, asulphonyl group, a carbonyl group, oxygen or sulphur,

e=the number 0 or 1,

Z represents F, Cl, Br or C₁ -C₄ alkyl and several Z's in one arylradical are the same or different,

d=the integers 0 or 1 to 4,

f=the integers 0 or 1 to 3.

It is particularly preferred to use compounds of formula II in which e=1and A' is a single bond, the 2,2-propylene radical or sulphur and d=0,but more especially 2,2-bis-(4-hydroxy phenyl)-propane and4,4'-dihydroxy diphenyl.

Preferred triaryl phosphates correspond to the following formula:##STR17## in which Z and m are as defined for formula I. It isparticularly preferred to use triphenyl phosphate.

Preferred trihydroxy and tetrahydroxy compounds are phloroglucinol;4,6-dimethyl-2,4,6-tri-(4-hydroxy phenyl)-2-heptene;4,6-dimethyl-2,4,6-tri-(4-hydroxy phenyl)-heptane; 1,3,5-tri-(4-hydroxyphenyl)-benzene; 1,1,1-tri-(4-hydroxy phenyl)-ethane; tri-(4-hydroxyphenyl)-phenyl methane; 2,2-bis-[4,4-bis-(4-hydroxyphenyl)-cyclohexyl]-propane; 2,4-bis-(4-hydroxy phenyl)-isopropylphenol; 2,6-bis-(2'-hydroxy-5'-methyl benzyl)-4-methyl phenol;2-(4-hydroxy phenyl)-2-(2,4-dihydroxy phenyl)-propane; tetra-(4-hydroxyphenyl)-methane; tetra-[4-(4-hydroxy phenyl isopropyl)-phenoxy]-methaneand 1,4-bis-(4,4"-dihydroxy triphenyl methyl)-benzene or mixturesthereof.

Basic catalysts which may be used for the transesterification reactioninclude:

alcoholates of the alkali or alkaline earth metals, such as sodiummethylate or calcium methylate;

sodium, potassium or lithium phenolates of monofunctional phenols;

sodium, potassium or lithium salts of the above-mentioned aromaticdihydroxy compounds corresponding to general formulae II and III;

hydrides of the alkali or alkaline earth metals, such as lithiumhydride, sodium borohydride or calcium hydride; oxides of the alkali andalkaline earth metals, such as lithium oxide, sodium oxide or bariumoxide; amides of the alkali and alkaline earth metals, such as sodiumamide or calcium amide, and basically reacting salts of the alkali oralkaline earth metals with organic or inorganic acids, such as sodiumacetate, sodium benzoate or sodium carbonate.

Imidazole is also suitable. Mixtures of the above-mentioned catalystsmay also be used. However, it is preferred to use monofunctional alkalimetal phenolates, such as sodium phenolate.

The basic catalysts are preferably used in quantities of from 7.10⁻⁴ to2.10⁻³ mole percent, based on 100 mole percent of aromatic dihydroxycompound.

All of the starting materials used for the transesterification reactionshould have purities of more than 99.1% and preferably of more than99.7%.

To carry out the process according to the invention, the phosphonic aciddiaryl esters and, optionally, triaryl phosphates are reacted with thearomatic dihydroxy compounds which may be mixed with trihydroxy ortetrahydroxy compounds in an oxygen-free atmosphere, i.e. in thepresence of an inert gas, such as nitrogen or carbon dioxide forexample, and in the presence of the above-mentioned basic catalysts attemperatures in the range of from 90° to 340° C., and, moreparticularly, at temperatures in the range from 150° to 320° C. Whilethe volatile aromatic monohydroxy aryls are distilled off at elevatedtemperature, preferably in vacuo, the reaction is continued withintroduction of inert gas until the required degree of condensation isreached.

By adding a base-binding substance, such as for example dimethylsulphate, diethyl sulphate, benzoyl chloride or phenyl chloroformic acidester, it is possible to neutralise the basic catalyst towards the endof the reaction in the polymer melt. The volatile neutralisationproducts formed may be removed from the melt by distillation in vacuo.After the catalyst has been neutralised, the transesterificationreaction may be continued to a limited extent in order to reach arequired molecular weight.

On completion of the polycondensation reaction, the polyphosphonate meltformed is converted in the usual way into granulates or directly intoshaped structures, such as films, fibres or bristles. Thepolyphosphonates thus obtained may be processed in the melt in standardprocessing machines, such as extruders and injection-moulding machines,into products characterised by extreme flame resistance and high thermalstability under load. Other valuable properties of the polyphosphonatesaccording to the invention are their excellent mechanical properties,such as for example their extreme toughness and their high tensilestrength.

The thermoplastic, aromatic branched polyphosphonates according to theinvention have relative viscosities of from 1.20 to more than 2.0 andpreferably from 1.24 to 1.40, as measured on a 0.5% by weight solutionin methylene chloride at 25° C.

The polyphosphonates according to the invention are soluble in methylenechloride; 1,1,2,2-tetrachloroethane; trichloroethylene; chloroform;chlorobenzene; 1,2-dichlorobenzene; dioxane and hexamethyl phosphoricacid triamide (HMPT).

Antistatic agents, pigments, mould release agents, heat stabilisers, UVstabilisers, fillers such as for example talcum, mineral wool, mica,calcium carbonate, dolomite and others, and also reinforcing fillers,such as for example glass fibres, glass beads and asbestos, may be addedto and mixed with the polyphosphonates.

The thermoplastic, aromatic, branched, preferably halogen-freepolyphosphonates according to the invention may be used for anyapplications where thermoplastic chemical materials of very high flameresistance are required and where, in addition, it is desired to avoidthe evolution of toxic pyrolysis gases under the effect of very hightemperatures. Applications such as these may be found for example invehicle construction, in aircraft construction, in the space sector orin the safety field.

The thermoplastic, aromatic polyphosphonates obtained by the processaccording to the invention as described above were extruded into testspecimens at 240° to 320° C.

Their behaviour under impact stressing was tested both by measuringimpact strength according to Charpy a_(n) in accordance with DIN No. 53453 or ASTM D No. 256 and by measuring notched impact strength accordingto Charpy a_(k) in accordance with DIN No. 53 453 or ASTM D 256.Hardness was measured by measuring the ball indentation hardness HK inaccordance with DIN No. 53 456. The mechanical-elastic properties weretested by strain-deformation tests, for example by measuring theE-modulus in bend in accordance with DIN No. 53 457, by measuring theE-modulus in tension in accordance with DIN No. 53 457, by measuringultimate tensile strength σ_(R), elongation at break ε_(R), yieldstrength σ_(S) and elongation at yield, ε_(S) in accordance with DIN No.53 455 (1968) or ASTM D 882.

Thermal stability under load was tested by measuring the Vicat softeningpoint (VSP) in accordance with DIN No. 53 460 or ISO/R 75. Thesecond-order transition temperatures T_(E) were determined bydifferential thermoanalysis (DTA).

Fire resistance was tested both by measuring the O₂ index in accordancewith ASTM D 2863-70 and also by measuring the after-burning time inaccordance with the UL test (Subject 94).

For these tests, test bars measuring 127×12.7×1.6 mm (1/16") and127×12.7×3.2 mm (1/8") were produced by injection moulding at 300° to310° C. These test bars were subjected to the test defined in Bulletin94 of Underwriters Laboratories, Inc. (Burning Test for ClassifyingMaterials).

In this test, the tested materials are given classifications of UL-94V-O, UL-94 V-I and UL-94 V-II on the basis of the results obtained withthe ten test specimens. Briefly, the criteria for each of these UL-94V-classifications are as follows:

UL-94 V-O: the average burning and/or glowing time after removal of theignition flame should not exceed 5 seconds and none of the testspecimens should release any drips which ignite absorbent cotton wool.

UL-94 V-I: the average burning and/or glowing time after removal of theignition flame should not exceed 25 seconds and none of the testspecimens should release any drips which ignite absorbent cotton wool.

UL-94 V-II: the average burning and/or glowing time after removal of theignition flame should not exceed 25 seconds and the test specimensrelease flaming particles which ignite absorbent cotton wool.

In addition, a test bar which burnt for more than 25 seconds afterremoval of the ignition flame is not classified under UL-94, but insteadis said to "burn" under the standard conditions of the presentinvention. A further requirement of the UL-94 test is that all the testbars used for one and the same test must achieve the particularV-classification, otherwise the ten best bars received theclassification of the worst individual bar. If for example one barachieves the classification UL-94 V-II and the other nine test bars theclassification UL-94 V-O, all ten bars are given the classificationUL-94 V-II.

EXAMPLE 1

6204 g (25.02 moles) of methyl phosphonic acid diphenyl ester, 4424 g(23.78 moles) of 4,4'-dihydroxy diphenyl, 7.6 g (1.21.10⁻² moles) of1,4-bis(4,4"-dihydroxy triphenyl methyl)-benzene and 0.2 g (1.72.10⁻³moles) of sodium phenolate are intensively mixed under nitrogen at 250°C. in an autoclave. Phenol is distilled off through a column heated to100° C. over a period of three hours under a vacuum falling from 250 to100 mbar and at a temperature increasing from 250° C. to 265° C. Thetransesterification reaction is then continued for 5 hours under apressure gradually falling to 0.3 mbar and at an internal temperatureincreasing to 310° C., the viscosity of the melt increasing. Theautoclave is purged with nitrogen, the polymer is left to sediment for 1hour at 300° C. with the stirrer switched off and the product isisolated by spinning off under pressure (approximately 10 atmospheres)and granulating the melt strand. A high molecular weight amorphouspolyphosphonate having a molecular weight (number average M_(n)) of27,600 and a relative viscosity η_(rel) of 1.321 (as measured on a 0.5%by weight solution in methylene chloride at 25° C.) is obtained in ayield of 5.2 kg. P=12.6% by weight. Flame resistance values andmechanical properties of the polyphosphonate according to Example 1:

    ______________________________________                                        Test           Test Standard  Test Value                                      ______________________________________                                        O.sub.2 -index ASTM-D 2863-70 75%                                             UL-test (Subject 94)          VO (1/16")                                                                    after burn-                                                                   ing time:                                                                     0 second                                        Vicat B        DIN 53 460     130° C.                                  Impact strength a.sub.n                                                                      DIN 53 453     unbroken                                        Notched impact DIN 53 453     32                                              strength a.sub.k                                                              Ball indentation                                                                             DIN 53 456     102 MPa                                         hardness HK                                                                   E-modulus in bend                                                                            DIN 53 457     2610 MPa                                        Flexural strength                                                                            DIN 53 457     59 MPa                                          E-modulus in tension                                                                         DIN 53 457     2420 MPa                                        Yield strength σ.sub.S                                                                 DIN 53 455 (1968)                                                                            56 MPa                                          Elongation at  DIN 53 455     8%                                              yield ε.sub.S                                                         Ultimate tensile                                                                             DIN 53 455     44 MPa                                          strength σ.sub.R                                                        Elongation at break ε.sub.R                                                          DIN 53 455     21%                                             ______________________________________                                    

EXAMPLE 2

774.4 g (3.12 moles) of methyl phosphonic acid diphenyl ester, 677.0 g(2.97 moles) of 2,2-bis(4-hydroxy phenyl)-propane (=bisphenol A), 9.4 g(1.5.10⁻² moles) of 1,4-bis-(4,4"-dihydroxy triphenyl methyl)-benzeneand 0.1 g (8.62.10⁻⁴ moles) of sodium phenolate are transesterified inthe melt as described in Example 1. 0.77 kg of a polyphosphonate havingthe following values are obtained:

Molecular weight (number average M_(n))=21,400

Relative solution viscosity η_(rel) =1.270 (as measured on a 0.5% byweight solution in methylene chloride at 25° C.)

P=10.7% by weight.

The amorphous polymer has a second order transition temperature T_(E) of90° C., as determined by DTA (=differential thermoanalysis).

EXAMPLE 3

155.10 g (0.639 mole) of methyl phosphonic acid diphenyl ester, 88.56 g(0.472 mole) of 4,4'-dihydroxy diphenyl, 31.90 g (0.1187 mole) of1,1-bis-(4-hydroxy phenyl)-cyclohexane, 0.19 g (0.304.10⁻³ mole) of1,4-bis-(4,4"-dihydroxy triphenyl methyl)-benzene and 5 mg (0.304.10⁻⁴mole) of sodium phenolate are transesterified in the melt as describedin Example 1. 150 g of an amorphous polyphosphonate having the followingvalues are obtained:

    ______________________________________                                        --M.sub.n                                                                             = 29,100       measured by methods described in                                              Examples 1 and 2                                       η.sub.rel                                                                         = 1.350                                                               P       = 11.9% by weight                                                     T.sub.E = 137° C. (as determined by DTA)                           

EXAMPLE 4

336 g (1.0 mole) of 2-phenyl ethylene phosphonic acid diphenyl ester,185.8 g (0.999 mole) of 4,4'-dihydroxy diphenyl, 0.626 g (1.10⁻³ mole)of 1,4-bis(4,4"-dihydroxy phenyl methyl)-benzene and 10 mg (0.765.10⁻⁴mole) of potassium phenolate are reacted as described in Example 1. 520g of a high molecular weight amorphous polyphosphonate having thefollowing values are obtained:

    ______________________________________                                        --M.sub.n                                                                             = 15,100       measured by the methods described in                                          Examples 1 and 2                                       η.sub.rel                                                                         = 1.221                                                               P       = 9.7% by weight                                                      T.sub.E = 140° C. (as determined by DTA)                               O.sub.2 index                                                                         = 58% (as determined in accordance with ASTM-D                                    2863-70)                                                      

COMPARISON EXAMPLE 1

Example 1 of U.S. Pat. No. 3,919,363 was repeated exactly. The polymerwas isolated by precipitation in methanol. The poly-(sulphonyldiphenylene)-phenyl phosphonate thus obtained has an average molecularweight (number average M_(n)) of 9,700, as determined by membraneosmosis, and a relative solution viscosity η_(rel) of 1.164 (as measuredon a 0.5% solution in methylene chloride at 25° C.). The residualcontent of hydrolysable chlorine amounted to 130 ppm; T_(E) =151° C. (asdetermined by DTA). The film prepared from a solution of this polymer inmethylene chloride is brittle. The polymer can be thermoplasticallyprocessed into hard and extremely brittle mouldings which actually breakon removal from the mould. Because of its low molecular weight and itshigh residual content of hydrolysable terminal chlorine groups, thispolymer is unsuitable for use as a thermoplastic material.

COMPARISON EXAMPLE 2

Example 2 of U.S. Pat. No. 2,682,522 was repeated exactly. Thepoly-(resorcinyl)-phenyl phosphonate thus obtained had an averagemolecular weight (number average M_(n)) of 7600, as determined bymembrane osmosis, and a relative solution viscosity η_(rel) of 1.147 (asmeasured on a 0.5% solution in methylene chloride at 25° C.). Theinorganic chlorine content amounted to 70 ppm. Because of its lowmolecular weight, the polymer was extremely brittle and was thereforeunsuitable for use as a thermoplastic material.

EXAMPLE 5

3100 g (12.5 moles) of methyl phosphonic acid diphenyl ester, 3.35 g(1.03.10⁻² moles) of triphenyl phosphate, 2216.2 g (11.92 moles) of4,4'-dihydroxy diphenyl and 0.1 g (0.862.10⁻³ mole) of sodium phenolatewere transesterified in the melt as described in Example 1. 2.6 kg of anamorphous polyphosphonate having the following values are obtained:

M_(n) =28,800

η_(rel) =1.332

P=12.6% by weight

Vicat-B temperature (DIN No. 53 460): 130° C.

EXAMPLE 6

3102 g (12.51 moles) of methyl phosphonic acid diphenyl ester, 1.7 g(0.52.10⁻² moles) of triphenyl phosphate, 2.44 g (0.39.10⁻² moles) of1,4-bis-(4,4"-dihydroxy triphenyl methyl)-benzene, 2214.7 g (11.91moles) of 4,4'-dihydroxy diphenyl and 0.1 g (0.862.10⁻³ moles) of sodiumphenolate are transesterified in the melt as described in Example 1. 2.6kg of an amorphous polyphosphonate having the following values areobtained:

M_(n) =27,700

η_(rel) =1.324

P=12.6% by weight

Vicat-B temperature (DIN No. 53 460): 130° C.

Comparison Examples 3 and 4 with U.S. Pat. No. 2,716,101 COMPARISONEXAMPLE 3

Example 3 of U.S. Pat. No. 2,716,101 was repeated exactly. Resorcinol,heptane phosphonyl dichloride and 5 mole percent of phosphorusoxychloride (based on 100 mole percent of heptane phosphonyl dichloride)were reacted at temperatures of up to 150° C. in the presence ofanhydrous magnesium chloride, the reaction being accompanied by theelimination of hydrogen chloride. Towards the end of the reaction, thereaction mixture could no longer be stirred. After cooling, theresulting polymer was very brittle and did not dissolve in dioxane,methylene chloride or chlorobenzene. Neither the molecular weight northe relative solution viscosity of this polymer could be measuredbecause of its high degree of crosslinking and its resultinginsolubility. The polymer obtained contained 870 ppm of hydrolysablechlorine. In view of its high content of hydrolysable chlorine, itsbrittleness and its high degree of crosslinking, this polymer isunsuitable for use as a thermoplastic chemical material.

COMPARISON EXAMPLE 4

Example 3 of U.S. Pat. No. 2,716,101 was repeated, the heptanephosphonyl dichloride being substituted by an equimolar quantity ofmethane phosphonyl dichloride.

Towards the end of the reaction, the resulting polymer could no longerbe stirred. After cooling, it was brittle and did not dissolve indioxane, methylene chloride or chlorobenzene. The polymer contained 420ppm of hydrolysable chlorine. Neither the molecular weight nor therelative solution viscosity of the polymer could be measured on accountof its high degree of crosslinking and its resulting insolubility. Thepolymer cannot be thermoplastically processed.

We claim:
 1. A process for the production of a thermoplastic branched,aromatic polyphosphonate having a number average molecular weight ofabove 11,000 said process comprising transesterifying components (a) and(b) with (c) and (d) wherein component (a) is from 97 to 100 moles of atleast one diaryl phosphonate and component (b) is up to 3 moles of atleast one triaryl phosphate with the sum of the moles of (a) and (b)being 100, component (c) is from 90 to 99 moles of at least one aromaticdihydroxy compound and component (d) is up to 3 moles of at least onearomatic trihydroxy or tetrahydroxy compound with the proviso that atleast one of the components (b) and (d) is present in a quantity of atleast 0.001 mole and that the combined amount of (b) and (d) is at most3 moles;said transesterification being conducted in the melt at 90° C.to 340° C. in an oxygen-free atmosphere at atmospheric pressure or lowerand in the presence of from 10⁻⁵ to 5×10⁻² mole percent, based on 100mole percent of aromatic dihydroxy compound, of at least one basiccatalyst, with the volatile constituents produced in the course oftransesterification being removed by distillation.
 2. The processaccording to claim 1 wherein the diaryl phosphonate of component (a) isof the formula ##STR18## wherein R¹ is alkyl having 1 to 12 carbonatoms, alkenyl having 2 to 12 carbon atoms, cycloalkyl having 6 to 30carbon atoms, cycloalkenyl having 6 to 30 carbon atoms, aryl having 6-30carbon atoms, arylalkyl having 6-30 carbon atoms or arylalkenyl having6-30 carbon atoms wherein each aryl moiety is unsubstituted orsubstituted by at least one halogen or alkyl having 1 to 4 carbonatoms;Z is fluoro, chloro, bromo or alkyl having 1 to 4 carbon atoms andwhen more than one Z occurs on one aryl moiety they may be the same ordifferent; and m is zero or an integer of from 1 to
 5. 3. The processaccording to claim 2 wherein R¹ is methyl or phenyl and m is zero. 4.The process according to claim 1 wherein the aromatic dihydroxy compoundof component (c) is of the formula ##STR19## wherein A' is a singlecovalent bond, alkylene having 1 to 4 carbon atoms, cycloalkylene having5 or 6 carbon atoms, sulphonyl, carbonyl, oxygen or sulphur;e is zero orthe number 1; Z is fluoro, chloro, bromo or alkyl having 1 to 4 carbonatoms and when more than one Z occurs on one aryl moiety they may be thesame or different; d is zero or an integer of from 1 to 4; and f is zeroor an integer of from 1 to
 3. 5. The process as claimed in claim 4wherein d is zero; e is the number 1; and A' is a single covalent bond,a 2,2-propylene moiety or sulphur.
 6. The process as claimed in claim 1wherein the aromatic trihydroxy or tetrahydroxy compound is selectedfrom the group consisting of phloroglucinol;4,6-dimethyl-2,4,6-tri-(4-hydroxy phenyl)-2-heptene;4,6-dimethyl-2,4,6-tri-(4-hydroxy phenyl)-heptane; 1,3,5-tri-(4-hydroxyphenyl)-benzene; 1,1,1-tri-(4-hydroxy phenyl)-ethane; tri-(4-hydroxyphenyl)phenyl methane; 2,2-bis-[4,4-bis-(4-hydroxyphenyl)-cyclohexyl]-propane; 2,4-bis-(4-hydroxy phenyl)-isopropylphenol; 2,6-bis-(2-hydroxy-5'-methyl benzyl)-4-methyl phenol;2-(4-hydroxy phenyl)-2-(2,4-dihydroxy phenyl)-propane; tetra-(4-hydroxyphenyl)-methane; tetra-[4-(4-hydroxy phenyl isopropyl)-phenoxy]-methane;1,4-bis-(4,4"-dihydroxy triphenyl methyl)-benzene and mixtures thereof.7. The process according to claim 1 wherein the triaryl phosphate ofcomponent (b) is of the formula ##STR20## wherein Z is fluoro, chloro,bromo or alkyl having 1 to 4 carbon atoms and when more than one Zoccurs on one aryl moiety they may be the same or different; andm iszero or an integer of from 1 to
 5. 8. The process according to claim 1wherein the triaryl phosphate is triphenyl phosphate.
 9. A thermoplasticmolding composition comprising the polyphosphonate prepared according toclaim 1 or said polyphosphonate admixed with at least one antistaticagent, pigment, mould release agent, heat stabilizer, UV stabilizer,filler or reinforcing fiber.